<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var age=18;
        const PI=3.14//不能更改,声明的常量必须赋值
        const user={
            name:'ajksd',
            age:18
        }
        user.age=30;
        console.log(user)//对象的值可以修改，数组里的值也可以修改
        //let取代var
        //let为块级作用域
    </script>
</body>
</html>